1. Field of the Invention
The present invention is directed to composite column and beam framing members for use in building construction. More particularly, the present invention is directed to a composite column or beam and a method for its manufacture that has superior insulating and fire/heat resistance characteristics.
2. Reference to Related Art
It is well known that the steel beams and columns that are used as the structural framework of modem buildings are not fireproof. Indeed, when exposed to heat and fire, steel beams and columns will expand, warp and rapidly lose strength. To protect against this type of extreme structural damage as well as the ongoing effects of weather, modem building codes often require that a coating of protective material be applied to the exterior surface of a building's steel framework. These protective materials are typically classified as either fire-resistant materials (i.e. mineral wool, fiberglass or the like) or heat sink materials (e.g. gypsum board or cement plasters). However, additional types of thermal or weather insulation may also be thought of as protective materials. Either class of fire-protective material can, for a reasonable period of time (e.g., one to three hours), be designed to delay the heat from a fire from affecting the steel framework.
Reinforced concrete framing systems, either pour-in-place or precast/prefabricated systems, do offer some known advantages over steel framing systems in the area of fire protection. However, columns and beams constructed of reinforced concrete have the notable disadvantage of being larger and heavier than steel framing members with the same capacity. Additionally, reinforced concrete systems necessarily require the builder to use concrete forms as part of the construction process. The erection, installation and removal of those forms can add significant cost (in time and labor) to any construction project.
Composite beam and column framing members that combine steel and concrete represent a compromise between pure steel or concrete building framing systems and are known in the art. One example is U.S. Pat. No. 4,333,285, which discloses a concrete column encased in a unitary steel tube. The column is adapted to support a reinforced concrete beam that is sheathed in a steel shell.
U.S. Pat. No. 4,409,764 discusses the use of steel column and beam forms that include internal metal reinforcing skeletons. The forms are prepared at an off-site factory and subsequently erected at the building site. The steel forms are filled with concrete at the building site and remain in place as a permanent part of the building framework.
Finally, U.S. Pat. No. 5,678,375 discusses a building framework that includes a number of structural steel members that each has a hollow interior. The steel members have openings that permit the hollow interiors to be filled with concrete in conjunction with the construction of the building frame.
Composite columns and beams are generally stronger than concrete framing members of similar size and are lighter than steel framing members. However, composite framing members still suffer from an increased risk of damage as a result of exposure to heat and flame. Therefore, it would be beneficial to provide improved composite column and beam framing members that have superior insulating, thermal and/or fire resistance characteristics.